This invention relates to an improved elevator assembly adapted for use with a well drilling apparatus in order to lift drilling tubulars quickly and efficiently.
In a wide variety of well drilling operations, it is necessary to assemble a drill string from a large number of individual lengths of drill pipe as a borehole is being drilled. When it becomes necessary for any reason to remove the drill string from the borehole, as for example to replace a worn drill bit, the drill string must be progressively raised as successive lengths of drill pipe are brought to the surface and removed from the drill string. Well servicing requires similar equipment, which, in smaller sizing, is used to pull or replace sucker rods, production piping, etc., for pump service, replacement of worn pipes or rods, or during well cleanout to improve production.
One type of drilling apparatus in wide-spread use utilizes a power swivel which is threadedly coupled to the uppermost length of drill pipes and then used to raise the drill string and to remove the uppermost length of drill pipe from the string. Once this has been accomplished, the threaded connection between the power swivel and the uppermost length of drill pipe is broken, and means such as a transfer arm can then be used to move the length of drill pipe from the vertical position aligned with the borehole to a horizontal position at ground level.
This prior art approach to raising a drill string and successively removing lengths of drill pipe from the string is not entirely acceptable. It requires that the power swivel be threadedly coupled to each successive length of drill pipe, and that this threaded connection then be broken. These repeated threading and unthreading operations can significantly slow the rate at which drill pipe can be removed from a borehole. In addition, these threading and unthreading operations can cause undesirable wear on the threaded connections of the swivel and of the drill pipe.
It is therefore an object of this invention to provide an improved apparatus useful in removing drill pipe from a borehole, and in particular to provide such an apparatus which does not require threaded connections between the apparatus and the drill pipe, and which can be used to speed the rate at which drill pipe can be removed from a borehole.